Optical System for Collecting Distance Information Within a Field

ABSTRACT

An optical system for collecting distance information within a field is provided. The optical system may include lenses for collecting photons from a field and may include lenses for distributing photons to a field. The optical system may include lenses that collimate photons passed by an aperture, optical filters that reject normally incident light outside of the operating wavelength, and pixels that detect incident photons. The optical system may further include illumination sources that output photons at an operating wavelength.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/232,222 filed Sep. 24, 2015.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates generally to the field of optical sensors andmore specifically to a new and useful optical system for collectingdistance information in the field of optical sensors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a system.

FIG. 2 is a schematic representation in accordance with one variation ofthe system.

FIG. 3 is a schematic representation in accordance with one variation ofthe system.

FIG. 4 is a schematic representation in accordance with one variation ofthe system.

FIG. 5 is a schematic representation in accordance with one variation ofthe system.

FIG. 6 is a schematic representation in accordance with one variation ofthe system.

FIG. 7 is a schematic representation in accordance with one variation ofthe system.

FIG. 8 is a schematic representation in accordance with one variation ofthe system.

FIG. 9 is a flowchart representation in accordance with one variation ofthe system.

FIG. 10 is a schematic representation in accordance with one variationof the system.

FIG. 11 is a schematic representation in accordance with one variationof the system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of embodiments of the invention is notintended to limit the invention to these embodiments but rather toenable a person skilled in the art to make and use this invention.Variations, configurations, implementations, example implementations,and examples described herein are optional and are not exclusive to thevariations, configurations, implementations, example implementations,and examples they describe. The invention described herein can includeany and all permutations of these variations, configurations,implementations, example implementations, and examples.

1. One-Dimensional Optical System: Aperture Array

As shown in FIG. 1, a one-dimensional optical system 100 for collectingdistance information within a field includes: a set of illuminationsources 110 arranged along a first axis, each illumination source in theset of illumination sources 110 configured to output an illuminatingbeam of an operating wavelength toward a discrete spot in the fieldahead of the illumination source; a bulk imaging optic 130 characterizedby a focal plane opposite the field; an aperture layer 140 coincidentthe focal plane, defining a set of apertures 144 in a line arrayparallel to the first axis, and defining a stop region 146 around theset of apertures 144, each aperture in the set of apertures 144 defininga field of view in the field coincident a discrete spot output by acorresponding illumination source in the set of illumination sources110, the stop region 146 absorbing light rays reflected from surfaces inthe field outside of fields of view defined by the set of apertures 144and passing through the bulk imaging optic 130; a set of lenses 150,each lens in the set of lenses 150 characterized by a second focallength, offset from the focal plane opposite the bulk imaging optic 130by the second focal length, aligned with an aperture in the set ofapertures 144, and configured to collimate light rays passed by theaperture; an optical filter 160 adjacent the set of lenses 150 oppositethe aperture layer 140 and configured to pass light rays at theoperating wavelength; a set of pixels 170 adjacent the optical filter160 opposite the set of lenses 150, each pixel in the set of pixels 170corresponding to a lens in the set of lenses 150 and including a set ofsubpixels arranged along a second axis non-parallel to the first axis;and a diffuser 180 interposed between the optical filter 160 and the setof pixels 170 and configured to spread collimated light output from eachlens in the set of lenses 150 across a set of subpixels of acorresponding pixel in the set of pixels 170.

1.1 Applications

Generally, the one-dimensional optical system 100 (the “system”)functions as an image sensor that, when rotated about an axis parallelto a column of apertures, collects three-dimensional distance data of avolume occupied by the system. Specifically, the one-dimensional opticalsystem 100 can scan a volume to collect three-dimensional distance datathat can then be reconstructed into a virtual three-dimensionalrepresentation of the volume, such as based on recorded times betweentransmission of illuminating beams from the illumination sources anddetection of photons—likely originating from the illuminationsources—incident on the set of pixels 170, based on phase-basedmeasurements techniques, or based on any other suitable distancemeasurement technique. The system 100 includes: a column of offsetapertures arranged behind a bulk imaging optic 130 and defining discretefields of view in a field ahead of the bulk imaging optic 130 (that isnon-overlapping fields of view beyond a threshold distance from thesystem); a set of illumination sources 110 that project discreteilluminating beams at an operating wavelength into (and substantiallyonly into) the fields of view defined by the apertures; a column oflenses that collimate light rays passed by corresponding apertures; andan optical filter 160 that selectively passes a narrow band ofwavelengths of light (i.e., electromagnetic radiation) including theoperating wavelength; and a set of pixels 170 that detect incidentphotons (e.g., count incident photons, tracks times between consecutiveincident photons). The system can therefore selectively projectilluminating beams into a field ahead of the system according to anillumination pattern that substantially matches—in size and geometryacross a range of distances from the system—the fields of view of theapertures. In particular, the illumination sources are configured toilluminate substantially only surfaces in the field ahead of the systemthat can be detected by pixels in the system such that minimal poweroutput by the system (via the illumination sources) is wasted byilluminating surfaces in the field for which the pixels are blind. Thesystem can therefore achieve a relatively high ratio of output signal(i.e., illuminating beam power) to input signal (i.e., photons passed toan incident on the pixel array). Furthermore, the set of lenses 150 cancollimate light rays passed by adjacent apertures such that light raysincident on the optical filter 160 meet the optical filter 160 at anangle of incidence of approximately 0°, thereby maintaining a relativelynarrow band of wavelengths of light passed by the optical filter 160 andachieving a relatively high signal-to-noise ratio (“SNR”) for light raysreaching the set of pixels 170.

The system includes pixels arranged in a column and aligned with theapertures, and each pixel can be non-square in geometry (e.g., short andwide) to extend the sensing area of the system for a fixed aperturepitch and pixel column height. The system also includes a diffuser 180that spreads light rays passed from an aperture through the opticalfilter 160 across the area of a corresponding pixel such that the pixelcan detect incident photons across its full width and height therebyincreasing the dynamic range of the system.

The system is described herein as projecting electromagnetic radiationinto a field and detecting electromagnetic radiation reflected from asurface in the field back to bulk receiver optic. Terms “illuminationbeam,” “light,” “light rays,” and “photons” recited herein refer to suchelectromagnetic radiation. The term “channel” recited herein refers toone aperture in the aperture layer 140, a corresponding lens in the setof lenses 150, and a corresponding pixel in the set of pixels 170.

1.2 Bulk Imaging Optic

The system includes a bulk imaging optic 130 characterized by a focalplane opposite the field. Generally, the bulk imaging optic 130functions to project incident light rays from outside the system towardthe focal plane where light rays incident on a stop region 146 of theaperture layer 140 are rejected (e.g., mirrored or absorbed) and wherelight rays incident on apertures in the aperture layer 140 are passedinto a lens characterized by a focal length and offset from the focalplane by the focal length.

In one implementation, the bulk imaging optic 130 includes a converginglens, such as a bi-convex lens (shown in FIG. 2) or a plano-convex lens,characterized by a particular focal length at the operating wavelengthof the system. The bulk imaging optic 130 can also include multiplediscrete lens that cooperate to project light rays toward the aperturelayer 140 and that are characterized by a composite focal plane oppositethe field, as shown in FIG. 11. However, the bulk imaging optic 130 canbe any other suitable type of lens or combination of lenses of any othertype or geometry.

1.3 Aperture Layer

As shown in FIGS. 1 and 2, the system includes an aperture layer 140coincident the focal plane, defining a set of apertures 144 in a linearray parallel to the axes of the illumination sources, and defining astop region 146 around the set of apertures 144, wherein each aperturein the set of apertures 144 defines a field of view in the fieldcoincident a discrete spot output by a corresponding illumination sourcein the set of illumination sources 110, and wherein the stop region 146absorbs and/or reflects light rays reflected from surfaces in the fieldoutside of fields of view defined by the set of apertures 144 andpassing through the bulk imaging optic 130. Generally, the aperturelayer 140 defines an array of open regions (i.e., apertures, includingone aperture per lens) and closed regions (“stop regions”) betweenadjacent opens. Each aperture in the aperture layer 140 defines a“pinhole” that defines a field of view for its corresponding sensechannel and passes light rights reflected from an external surfacewithin its field of the view into its corresponding lens, and each stopregion 146 can block light rays incident on select regions of the focalplane from passing into the lens array, as shown in FIG. 6.

The aperture layer 140 includes a relatively thin opaque structurecoinciding with (e.g., arranged along) the focal plane of the bulkimaging optic 130, as shown in FIGS. 1 and 2. For example, the aperturelayer 140 can include a 10 micrometer-thick copper, silver, or nickelfilm deposited (e.g., plated) over a photocurable transparent polymerand then selectively etched to form the array of apertures. In a similarexample, a reflective metalized layer or a light-absorbing photopolymer(e.g., a photopolymer mixed with a light absorbing dye) can be depositedonto a glass wafer and selectively cured with a photomask to form theaperture layer 140 and the set of apertures 144. Alternatively, theaperture layer 140 can include a discrete metallic film that ismechanically or chemically perforated to form the array of apertures,bonded to the lens array, and then installed over the bulk imaging optic130 along the focal plane. However, the aperture layer 140 can includeany other reflective (e.g., mirrored) or light-absorbing material formedin any other way to define the array of apertures along the focal planeof the bulk imaging optic 130.

In the one-dimensional optical system 100, the aperture layer 140 candefine a single column of multiple discrete circular apertures ofsubstantially uniform diameter, wherein each aperture defines an axissubstantially parallel to and aligned with one lens in the lens array,as shown in FIG. 3. Adjacent apertures are offset by an aperture pitchdistance greater than the aperture diameter and substantially similar tothe lens pitch distance, and the aperture layer 140 defines a stopregion 146 (i.e., an opaque or reflecting region) between adjacentapertures such that the apertures define discrete, non-overlappingfields of view for their corresponding sense channels. At increasinglysmaller diameters up to a diffraction-limited diameter—which is afunction of wavelength of incident light and numeric aperture of thebulk imaging lens—an aperture defines a narrower field of view (i.e., afield of view of smaller diameter) and passes a sharper butlower-intensity (attenuated) signal from the bulk imaging optic 130 intoits corresponding lens. The aperture layer 140 can therefore defineapertures of diameter: greater than the diffraction-limited diameter forthe wavelength of light output by the illumination sources (e.g., 900nm); substantially greater than the thickness of the aperture layer 140;and less than the aperture pitch distance, which is substantiallyequivalent to the lens pitch distance and the pixel pitch distance. Inone example, aperture layer 140 can define apertures of diametersapproaching the diffraction-limited diameter to maximize geometricalselectivity of the field of view of each sense channel. Alternatively,the apertures can be of diameter less that the diffraction-limiteddiameter for the wavelength of light output by the illumination sources.In one example, the aperture layer 140 can define apertures of diametersmatched to a power output of illumination sources in the system and to anumber and photon detection capacity of subpixel photodetectors in eachpixel in the set of pixels 170 to achieve a target number of photonsincident on each pixel within each sampling period. In this example,each aperture can define a particular diameter that achieves targetattenuation range for pixels originating from a correspondingillumination source and incident on the bulk imaging optic 130 during asampling period. In particular, because an aperture in the aperturelayer 140 attenuates a signal passed to its corresponding lens and on toits corresponding pixel, the diameter of the aperture can be matched tothe dynamic range of its corresponding pixel.

In one implementation, a first aperture 141 in the aperture layer 140passes light rays—reflected from a discrete region of a surface in thefield (the field of view of the sense channel) ahead of the bulk imagingoptic 130—into its corresponding lens; a stop region 146 interposedbetween the first aperture 141 and adjacent apertures in the aperturelayer 140 blocks light rays—reflected from a region of the surfaceoutside of the field of view of the first aperture 141—from passing intothe lens corresponding to the first aperture 141. In the one-dimensionaloptical system 100, the aperture layer 140 therefore defines a column ofapertures that define multiple discrete, non-overlapping fields of viewof substantially infinite depth of field, as shown in FIG. 2.

In this implementation, a first aperture 141 in the aperture layer 140defines a field of view that is distinct and that does not intersect afield of view defined by another aperture in the aperture layer 140, asshown in FIG. 2. The set of illumination sources 110 includes a firstillumination source 111 paired with the first aperture 141 andconfigured to project an illuminating beam substantially aligned with(i.e., overlapping) the field of view of the first aperture 141 in thefield ahead of the bulk imaging optic 130. Furthermore, the firstillumination source 111 and a bulk transmitting optic 120 can cooperateto project an illuminating beam of a cross-section substantially similarto (and slightly larger than) the cross section of the field of view ofthe first aperture 141 as various distances from the bulk imaging optic130. Therefore light output by the first illumination source 111—pairedwith the first aperture 141—and projected into the field of view of thefirst aperture 141 can remain substantially outside the fields of viewof other apertures in the aperture layer 140.

Generally, photons projected into the field by the first illuminationsource 111 illuminate a particular region of a surface (or multiplesurfaces) in the field within the field of view of the first sensechannel and are reflected (e.g., scattered) by the surface(s); at leastsome of these photons reflected by the particular region of a surfacemay reach the bulk imaging optic 130, which directs these photons towardthe focal plane. Because these photons were reflected by a region of asurface within the field of view of the first aperture 141, the bulkimaging optic 130 may project these photons into the first aperture 141,and the first aperture 141 may pass these photons into the first lens151 (or a subset of these photons incident at an angle relative to theaxis of the first aperture 141 below a threshold angle). However,because a second aperture 142 in the aperture layer 140 is offset fromthe first aperture 141 and because the particular region of the surfacein the field illuminated via the first illumination source 111 does not(substantially) coincide with the field of view of the second aperture142, photons reflected by the particular region of the surface andreaching the bulk imaging optic 130 are projected into the secondaperture 142 and passed to a second lens 152 behind the second aperture142, and vice versa, as shown in FIG. 2. Furthermore, a stop region 146between the first and second apertures 142 can block photons directedtoward the focal plane between the first and second apertures 142reflected by the bulk imaging optic 130, thereby reducing crosstalkbetween the first and second sense channels.

For a first aperture 141 in the aperture layer 140 paired with a firstillumination source 111 in the set of illumination sources 110, thefirst aperture 141 in the aperture layer 140 defines a first field ofview and passes—into the first lens 151—incident light rays originatingat or reflected from a surface in the field coinciding with the firstfield of view. Because the first illumination source 111 projects anilluminating beam that is substantially coincident (and substantiallythe same size as or minimally larger than) the field of view defined bythe first aperture 141 (as shown in FIG. 4), a signal passed into thefirst lens 151 by the first aperture 141 in the aperture layer 140 canexhibit a relatively high ratio of light rays originating from the firstillumination source 111 to light rays originating from otherillumination sources in the system. Generally, because variousillumination sources in the system may output illuminating beams atdifferent frequencies, duty cycles, and/or power levels, etc. at aparticular time during operation, light rays passed from the bulkimaging optic 130 into a first pixel 171 in the set of pixels 170 butoriginating from an illumination source other than the firstillumination source 111 paired with the first pixel 171 constitute noiseat the first pixel 171. Though the relatively small diameters ofapertures in the aperture layer 140 may attenuate a total light signalpassed from the bulk imaging optic 130 into the set of lenses 150, eachaperture in the aperture layer 140 may pass a relatively high proportionof photons originating from its corresponding illumination source thanfrom other illumination sources in the system; that is, due to thegeometry of a particular aperture and its corresponding illuminationsource, a particular aperture may pass a signal exhibiting a relativelyhigh SNR to its corresponding lens and thus into its correspondingpixel. Furthermore, at smaller aperture diameters in the aperture layer140—and therefore smaller fields of view of corresponding channels—thesystem can pass less noise from solar radiation or other ambient lightsources to the set of pixels 170.

In one variation, the system includes a second aperture layer interposedbetween the lens array and the optical filter 160, wherein the secondaperture layer defines a second set of apertures 144, each aligned witha corresponding lens in the set of lenses 150, as described above. Inthis variation, an aperture in the second aperture layer 140 can absorbor reflect errant light rays passed by a corresponding lens, asdescribed above, to further reduce crosstalk between channels, therebyimproving SNR within the system. Similarly, the system can additionallyor alternatively include a third aperture layer interposed between theoptical filter 160 and the diffuser(s) 180, wherein the third aperturelayer defines a third set of apertures 144, each aligned with acorresponding lens in the set of lenses 150, as described above. In thisvariation, an aperture in the third aperture layer can absorb or reflecterrant light rays passed by the light filter, as described above, toagain reduce crosstalk between channels, thereby improving SNR withinthe system.

1.4 Lens Array

The system includes a set of lenses 150, wherein each lens in the set oflenses 150 is characterized by a second focal length, is offset from thefocal plane opposite the bulk imaging optic 130 by the second focallength, is aligned with a corresponding aperture in the set of apertures144, and is configured to collimate light rays passed by thecorresponding aperture. Generally, a lens in the set of lenses 150functions to collimate lights rays passed by its corresponding apertureand to pass these collimated light rays into the optical filter 160.

In the one-dimensional optical system 100, the lenses are arranged in asingle column, and adjacent lenses are offset by a uniform lens pitchdistance (i.e., a center-to-center-distance between adjacent pixels), asshown in FIG. 3. The set of lenses 150 is interposed between theaperture layer and the optical filter 160. In particular, each lens caninclude a converging lens characterized by a second focal length and canbe offset from the focal plane of the bulk imaging optic 130—oppositethe bulk imaging optic 130—by the second focal length to preserve theaperture of the bulk imaging optic 130 and to collimate light incidenton the bulk imaging optic 130 and passed by a corresponding aperture.Each lens in the set of lens can be characterized by a relatively shortfocal length (i.e., less than a focal length of the bulk imaging optic130) and a relatively large marginal ray angle (e.g., a relatively highnumeric aperture lens) such that the lens can capture highly-angledlight rays projected toward the lens by the extent of the bulk imagingoptic 130. That is, each lens in the set of lens can be characterized bya ray cone substantially matched to a ray cone of the bulk imaging optic130.

Lenses in the set of lenses 150 can be substantially similar. A lens inthe set of lenses 150 is configured to collimate light rays focused intoits corresponding aperture by the bulk imaging optic 130. For example, alens in the set of lenses 150 can include a bi-convex or plano-convexlens characterized by a focal length selected based on the size (e.g.,diameter) of its corresponding aperture and the operating wavelength ofthe system. In this example, the focal length (f) of a lens in the setof lenses 150 can be calculated according to the formula:

$f = \frac{d^{2}}{2\lambda}$

where d is the diameter of the corresponding aperture in the aperturelayer and A is the operating wavelength of light output by theillumination source (e.g., 900 nm). The geometry of a lens in the set oflenses 150 can therefore be matched to the geometry of a correspondingaperture in the aperture layer such that the lens passes a substantiallysharp image of light rays—at or near the operating wavelength—into theoptical filter 160 and thus on to the pixel array.

However, the set of lenses 150 can include lenses of any other geometryand arranged in any other way adjacent the aperture layer.

1.5 Optical Filter

As shown in FIG. 3, the system includes an optical filter 160 adjacentthe set of lenses 150 opposite the aperture layer and configured to passlight rays at the operating wavelength. Generally, the optical filter160 receives electromagnetic radiation across a spectrum from the set oflenses 150, passes a relatively narrow band of electromagneticradiation—including radiation at the operating wavelength—to the pixelarray, and blocks electromagnetic radiation outside of the band. Inparticular, electromagnetic radiation other than electromagneticradiation output by the illumination source—such as ambientlight—incident on a pixel in the set of pixels 170 constitutes noise inthe system. The optical filter 160 therefore functions to rejectelectromagnetic radiation outside of the operating wavelength or, morepragmatically, outside of a narrow wavelength band, thereby reducingnoise in the system and increasing SNR.

In one implementation, the optical filter 160 includes an opticalbandpass filter that passes a narrow band of electromagnetic radiationsubstantially centered at the operating wavelength of the system. In oneexample, the illumination sources output light (predominantly) at anoperating wavelength of 900 nm, and the optical filter 160 is configuredto pass light between 899.95 nm and 900.05 nm and to block light outsideof this band.

The optical filter 160 may selectively pass and reject wavelengths oflight as a function of angle of incidence on the optical filter 160.Generally, optical bandpass filters may pass wavelengths of lightinversely proportional to their angle of incidence on the light opticalbandpass filter. For example, for an optical filter 160 including a 0.5nm-wide optical bandpass filter, the optical filter 160 may pass over95% of electromagnetic radiation over a sharp band from 899.75 nm to900.25 nm and reject approximately 100% of electromagnetic radiationbelow 899.70 nm and above 900.30 nm for light rays incident on theoptical filter 160 at an angle of incidence of approximately 0°.However, in this example, the optical filter 160 may pass over 95% ofelectromagnetic radiation over a narrow band from 899.5 nm to 900.00 nmand reject approximately 100% of electromagnetic radiation over a muchwider band below 899.50 nm and above 900.30 nm for light rays incidenton the optical filter 160 at an angle of incidence of approximately 15°.Therefore, the incidence plane of the optical filter 160 can besubstantially normal to the axes of the lenses, and the set of lenses150 can collimate light rays received through a corresponding apertureand output these light rays substantially normal to the incidence planeof the optical filter 160 (i.e., at an angle of incidence ofapproximately 0° on the optical filter). Specifically, the set of lenses150 can output light rays toward the optical filter 160 at angles ofincidence approximating 0° such that substantially all electromagneticradiation passed by the optical filter 160 is at or very near theoperating wavelength of the system.

In the one-dimensional optical system 100, the system can include asingle optical filter 160 that spans the column of lens in the set oflenses 150. Alternatively, the system can include multiple opticalfilters 160, each adjacent a single lens or a subset of lenses in theset of lenses 150. However, the optical filter 160 can define any othergeometry and can function in any other way to pass only a limited bandof wavelengths of light.

1.6 Pixel Array and Diffuser

The system includes a set of pixels 170 adjacent the optical filter 160opposite the set of lenses 150, each pixel in the set of pixels 170corresponding to a lens in the set of lenses 150 and including a set ofsubpixels arranged along a second axis non-parallel to the first axis.Generally, the set of pixels 170 are offset from the optical filter 160opposite the set of lenses 150, and each pixel in the set of pixels 170functions to output a single signal or stream of signals correspondingto the count of photons incident on the pixel within one or moresampling periods, wherein each sampling period may be picoseconds,nanoseconds, microseconds, or milliseconds in duration.

The system also includes a diffuser 180 interposed between the opticalfilter 160 and the set of pixels 170 and configured to spread collimatedlight output from each lens in the set of lenses 150 across a set ofsubpixels of a single corresponding pixel in the set of pixels 170.Generally, for each lens in the set of lenses 150, the diffuser 180functions to spread light rays—previously collimated by the lens andpassed by the optical filter 160—across the width and height of asensing area within a corresponding pixel. The diffuser 180 can define asingle optic element spanning the set of lenses 150, or the diffuser 180can include multiple discrete optical elements, such as including oneoptical diffuser element aligned with each channel in the system.

In one implementation, a first pixel 171 in the set of pixels 170includes an array of single-photon avalanche diode detectors(hereinafter “SPADs”), and the diffuser 180 spreads lightsrays—previously passed by a corresponding first aperture 141, collimatedby a corresponding first lens 151, and passed by the optical filter160—across the area of the first pixel 171, as shown in FIGS. 3, 5, and6. Generally, adjacent apertures can be aligned and offset vertically byan aperture pitch distance, adjacent lenses can be aligned and offsetvertically by a lens pitch distance substantially identical to theaperture pitch distance, and adjacent pixels can be aligned and offsetvertically by a pixel pitch distance substantially identical to the lensand aperture pitch distances. However, the pixel pitch distance mayaccommodate only a relatively small number of (e.g., two)vertically-stacked SPADs. Each pixel in the set of pixels 170 cantherefore define an aspect ratio greater than 1:1, and the diffuser 180can spread light rays passed by the optical filter 160 according to thegeometry of a corresponding pixel in order to accommodate a largersensing area per pixel.

In one example, each pixel in the set of pixels 170 is arranged on animage sensor, and a first pixel 171 in the set of pixels 170 includes asingle row of 16 SPADs spaced along a lateral axis perpendicular to avertical axis bisecting the column of apertures and lenses. In thisexample, the height of a single SPAD in the first pixel 171 can be lessthan the height (e.g., diameter) of the first lens 151, but the totallength of the 16 SPADs can be greater than the width (e.g., diameter) ofthe first lens 151; the diffuser 180 can therefore converge light raysoutput from the first lens 151 to a height corresponding to the heightof a SPAD at the plane of the first pixel 171 and can diverge light raysoutput from the first lens 151 to a width corresponding to the width ofthe 16 SPADs at the plane of the first pixel 171. In this example, theremaining pixels in the set of pixels 170 can include similar rows ofSPADs, and the diffuser 180 can similarly converge and diverge lightrays passed by corresponding apertures onto corresponding pixels.

In the foregoing example, the aperture layer can include a column of 16like apertures, the set of lenses 150 can include a column of 16 likelenses arranged behind the aperture layer, and the set of pixels 170 caninclude a set of 16 like pixels—each including a similar array ofSPADs—arranged behind the set of lenses 150. For a 6.4 mm-wide, 6.4mm-tall image sensor, each pixel can include a single row of 16 SPADs,wherein each SPAD is electrically coupled to a remote analog front-endprocessing electronics/digital processing electronics circuit 240. EachSPAD can be arranged in a 400 μm-wide, 400 μm-tall SPAD area and candefine an active sensing area approaching 400 μm in diameter. AdjacentSPADs can be offset by a SPAD pitch distance of 400 μm. In this example,the aperture pitch distance along the vertical column of apertures, thelens pitch distance along the vertical column of lenses, and the pixelpitch distance along the vertical column of pixels can each beapproximately 400 μm accordingly. For the first sense channel in thesystem (i.e., the first aperture 141, the first lens 151, and the firstpixel 171, etc.), a first diffuser 180 can diverge a cylindrical columnof light rays passed from the first lens 151 through the optical filter160—such as a column of light approximately 100 μm in diameter for anaperture layer aspect ratio of 1:4—to a height of approximately 400 μmaligned vertically with the row of SPADs in the first pixel 171. Thefirst diffuser can similarly diverge the cylindrical column of lightrays passed from the first lens 151 through the optical filter 160 to awidth of approximately 6.4 μm centered horizontally across the row ofSPADs in the first pixel 171. Other diffusers 180 in the system cansimilarly diverge (or converge) collimated light passed by correspondinglenses across corresponding pixels in the set of pixels 170. Therefore,in this example, by connecting each SPAD (or each pixel) to a remoteanalog front-end processing electronics/digital processing electronicscircuit 240 and by incorporating diffusers 180 that spread light passedby the optical filter 160 across the breadths and heights ofcorresponding pixels, the system can achieve a relatively high sensingarea fill factor across the imaging sensor.

Therefore, in the one-dimensional optical system 100, pixels in the setof pixels 170 can include an array of multiple SPADS arranged in aspectratio exceeding 1:1, and the diffuser 180 can spread light rays acrosscorresponding non-square pixels that enables a relatively large numbersof SPADs to be tiled across a single pixel to achieve a greater dynamicrange across the image sensor than an image sensor with a single SPADper pixel, as shown in FIG. 3. In particular, by incorporating multipleSPADs per pixel (i.e., per sense channel), a first sense channel in thesystem can detect multiple incident photons—originating from a surfacein the field bound by a field of view defined by the first aperture141—within the span of the dead time characteristic of the SPADs. Thefirst sense channel can therefore detect a “brighter” surface in itsfield of view. Additionally or alternatively, the first pixel 171 in thefirst sense channel can be sampled faster than the dead timecharacteristic of SPADs in the first pixel 171 because, though a firstsubset of SPADs in the first pixel 171 may be down (or “dead”) during afirst sampling period due to collection of incident photons during thefirst sampling period, other SPADs in the first pixel 171 remain on (or“alive”) and can therefore collect incident photons during a subsequentsampling period. Furthermore, by incorporating pixels characterized byrelatively high aspect ratios of photodetectors, the image sensor caninclude pixels offset by a relatively small pixel pitch, but the system100 can still achieve a relatively high dynamic range pixel.

However, pixels in the set of pixels 170 can include any other number ofSPADs arranged in any other arrays, such as in a 64-by-1 grid array (asdescribed above), in a 32-by-2 grid array, or in a 16-by-4 grid array,and the diffuser 180 can converge and/or diverge collimated light raysonto corresponding pixels accordingly in any other suitable way.Furthermore, rather than (or in addition to) SPADs, each pixel in theset of pixels 170 can include one or more linear avalanche photodiodes,Geiger mode avalanche photodiodes, photomultipliers, resonant cavityphotodiodes, QUANTUM DOT detectors, or other types of photodetectorsarranged as described above, and the diffuser(s) 180 can similarlyconverge and diverge signals passed by the optical filter(s) 160 acrosscorresponding pixels, as described herein.

1.7 Illumination Sources

The system includes a set of illumination sources 110 arranged along afirst axis, each illumination source in the set of illumination sources110 configured to output an illuminating beam of an operating wavelengthtoward a discrete spot in a field ahead of the illumination source.Generally, each illumination source functions to output an illuminatingbeam coincident a field of view defined by a corresponding aperture inthe set of apertures 144, as shown in FIGS. 1 and 2.

In one implementation, the set of illumination sources 110 includes abulk transmitter optic and one discrete emitter per sense channel. Forexample, the set of illumination sources 110 can include a monolithicVCSEL arrays including a set of discrete emitters. In thisimplementation, the bulk transmitter optic can be substantiallyidentical to the bulk imaging optic 130 in material, geometry (e.g.,focal length), thermal isolation, etc., and the bulk transmitter opticis adjacent and offset laterally and/or vertically from the bulk imagingoptic 130. In a first example, set of illumination sources 110 includesa laser array including discrete emitters arranged in a column withadjacent emitters offset by an emitter pitch distance substantiallyidentical to the aperture pitch distance. In this first example, eachemitter outputs an illuminating beam of diameter substantially identicalto or slightly greater than the diameter of a corresponding aperture inthe apertures layer, and the column of emitters is arranged along thefocal plane of the bulk transmitter optic such that each illuminatingbeam projected from the bulk transmitter optic into the field intersectsand is of substantially the same size and geometry as the field of viewof the corresponding sense channel, as shown in FIG. 4. Therefore,substantially all power output by each emitter in the set ofillumination sources 110 can be projected into the field of view of itscorresponding sense channel with relatively minimal power wastedilluminating surfaces in the field outside of the fields of view of thesense channels.

In a second example, the discrete emitters are similarly arranged in acolumn with adjacent emitters offset by an emitter pitch distance twicethe aperture pitch distance, as shown in FIG. 2. In this second example,each emitter is characterized by an illuminating active area (oraperture) of diameter approximately (or slightly greater than) twice thediameter of a corresponding aperture in the apertures layer, and thecolumn of emitters is offset behind the bulk transmitter optic by twicethe focal length of the bulk transmitter optic such that eachilluminating beam projected from the bulk transmitter optic into thefield intersects and is of substantially the same size and geometry asthe field of view of the corresponding sense channel, as describedabove. Furthermore, for the same illumination beam power density, anilluminating beam output by an emitter in this second example maycontain four times the power of an illuminating beam output by anemitter in the first example described above. The system can thereforeinclude a set of emitter arranged according to an emitter pitchdistance, configured to output illuminating beams of diameter, andoffset behind the bulk transmitter optic by an offset distance as afunction of a scale factor (e.g., 2.0 or 3.0) and 1) the aperture pitchdistance in the aperture layer, 2) the diameter of apertures in theaperture layer, and 3) the focal length of bulk transmitter optic,respectively. The system can therefore include an illuminating subsystemthat is proportionally larger than a corresponding receiver subsystem toachieve greater total output illumination power within the same beamangles and fields of view of corresponding channels in the receiversubsystem.

The system can also include multiple discrete sets of illuminationsources, each set of illumination sources 110 paired with a discretebulk transmitter optic adjacent the bulk imaging optic 130. For example,the system can include a first bulk transmitter optic, a second bulktransmitter optic, and a third bulk transmitter optic patterned radiallyabout the bulk imaging optic 130 at a uniform radial distance from thecenter of the bulk imaging optic 130 and spaced apart by an angulardistance of 120°. In this example, the system can include a laser arraywith one emitter—as described above—behind each of the first, second,and third bulk transmitter optics. Each discrete laser array and itscorresponding bulk transmitter optic can thus project a set ofilluminating beams into the fields of view of defined by correspondingin the apertures in the aperture layer. Therefore, in this example, thethree discrete laser arrays and the three corresponding bulk transmitteroptics can cooperate to project three times the power onto the fields ofview of the sense channels in the system, as compared to a single laserarray and one bulk transmitter optic. Additionally or alternatively, thesystem can include multiple discrete layer arrays and bulk transmitteroptics to both: 1) achieve a target illumination power output into thefield of view of each sensing channel in the receiver subsystem withmultiple lower-power emitters per sensing channel; and 2) distributeoptical energy over a larger area in the near-field to achieve anoptical energy density less than a threshold allowable optical energydensity for the human eye.

However, the system can include any other number and configuration ofillumination source sets and bulk transmitter optics configured toilluminate fields of view defined by the sense channels. The set ofillumination sources 110 can also include any other suitable type ofoptical transmitter, such as a 1×16 optical splitter powered by a singlelaser diode, a side-emitting laser diode array, an LED array, or aquantum dot LED array, etc.

1.8 Fabrication

In one implementation, the bulk receiver lens, the aperture layer, theset of lenses 150, the optical filter 160, and the diffuser 180 arefabricated and then aligned with and mounted onto an image sensor. Forexample, the optical filter 160 can be fabricated by coating a fusedsilica substrate. Photoactive optical polymer can then be deposited overthe optical filter 160, and a lens mold can be placed over thephotoactive optical polymer and a UV light source activated to cure thephotoactive optical polymer in the form of lenses patterned across theoptical filter 160. Standoffs can be similarly molded or formed acrossthe optical filter 160 via photolithography techniques, and an aperturelayer defined by a selectively-cured, metallized glass wafer can then bebonded or otherwise mounted to the standoffs to form the aperture layer.The assembly can then be inverted, and a set of discrete diffusers andstandoffs can be similarly fabricated across the opposite side of theoptical filter 160. A discrete image sensor can then be aligned with andbonded to the standoffs, and a bulk imaging optic 130 can be similarlymounted over the aperture layer.

Alternatively, photolithography and wafer level bonding techniques canbe implemented to fabricate the bulk imaging optics, the aperture layer,the set of lenses 150, the optical filter 160, and the diffuser 180directly on to the un-diced semiconductor wafer containing the detectorchips in order to simplify manufacturing, reduce cost, and reduceoptical stack height for decreased pixel crosstalk.

2. One-Dimensional Optical System: Lens Tube

One variation of the system includes: a set of illumination sources 110arranged along a first axis, each illumination source in the set ofillumination sources 110 configured to output an illuminating beam of anoperating wavelength toward a discrete spot in a field ahead of theillumination source; a bulk imaging optic 130 characterized by a focalplane opposite the field; a set of lens tubes 210 arranged in a linearray parallel to the first axis, each lens tube in the set of lenstubes 210 including: a lens characterized by a focal length, offset fromthe focal plane by the focal length, and configured to collimate lightrays reflected into the bulk imaging optic 130 from a discrete spot inthe field illuminated by a corresponding illumination source in the setof optics into the bulk imaging optic 130; and a cylindrical wall 218extending from the lens opposite the focal plane, defining a long axissubstantially perpendicular to the first axis, and configured to absorbincident light rays reflected into the bulk imaging optic 130 from aregion in the field outside the discrete spot illuminated by thecorresponding illumination source. In this variation, the system alsoincludes: an optical filter 160 adjacent the set of lens tubes 210opposite the focal plane and configured to pass light rays at theoperating wavelength; a set of pixels 170 adjacent the optical filter160 opposite the set of lenses 150, each pixel in the set of pixels 170corresponding to a lens in the set of lenses 150 and including a set ofsubpixels aligned along a third axis perpendicular to the first axis;and a diffuser 180 interposed between the optical filter 160 and the setof pixels 170 and configured to spread collimated light output from eachlens in the set of lenses 150 across a set of subpixels of acorresponding pixel in the set of pixels 170.

Generally, in this variation, the system includes a lens tube inreplacement of (or in addition to) each aperture and lens pair describedabove. In this variation, each lens tube can be characterized by asecond (short) focal length and can be offset from the focal plane ofthe bulk imaging optic 130 by the second focal length to preserve theaperture of the bulk imaging optic 130 and to collimate incident lightreceived from the bulk imaging optic 130, as described above and asshown in FIGS. 5 and 7.

Each lens tube also defines an opaque cylindrical wall 218 defining anaxis normal to the incidence plane of the adjacent optical filter 160and configured to absorb incident light rays, as shown in FIG. 5.Generally, at greater axial lengths, the cylindrical wall 218 of a lenstube may absorb light rays passing through the lens tube at shallowerangles to the axis of the lens tube, thereby reducing the field of viewof the lens tube (which may be similar to decreasing the diameter of anaperture in the aperture layer up to the diffraction-limited diameter,as described above) and yielding an output signal of collimated lightrays nearer to perpendicular to the incidence plane of the opticalfilter 160. Each lens tube can therefore define an elongated cylindricalwall 218 of length sufficient to achieve a target field of view and topass collimated light rays at maximum angles to the axis of the lenstube less than a threshold angle. In this variation, a lens tube canthus function as an aperture-sense pair described above to define anarrow field of view and to output substantially collimated light to theadjacent optical filter 160.

The cylindrical wall 218 of a lens tube can define a coarse or patternedopaque interface about a transparent (or translucent) lens material, asshown in FIG. 5, to increase absorption and decrease reflection of lightrays incident on the cylindrical wall 218. Each lens tube (and each lensdescribed above) can also be coated with an anti-reflective coating.

As shown in FIG. 9, in this variation, the set of lens tubes 210 can befabricated by implementing photolithography techniques to pattern aphotoactive optical polymer (e.g., SU8) onto the optical filter 160(e.g., on a silicon wafer defining the optical filter). Alight-absorbing polymer can then be poured between the lens tubes andcured. A set of lenses 150 can then be fabricated (e.g., molded)separately and then bonded over the lens tubes. Alternatively, lensescan be fabricated directly onto the lens tubes by photolithographytechniques. Yet alternatively, a mold for lenses can be cast directlyonto the lens tubes by injecting polymer into a mold arranged over thelens tubes. A singular diffuser 180 or multiple discrete diffusers 180can be similarly fabricated and/or assembled on the optical filter 160opposite the lens tubes. Standoffs extending from the optical filter 160can be similarly fabricated or installed around the diffuser(s) 180, andthe image sensor can be aligned with and bonded to the standoffsopposite the optical filter 160. Other optical elements within thesystem (e.g., the bulk imaging lens, the bulk transmitting lens, etc.)can be fabricated according to similar techniques and with similarmaterials.

3. Two-Dimensional Optical System

Another variation of the system includes: a set of illumination sources110 arranged in a first rectilinear grid array, each illumination sourcein the set of illumination sources 110 configured to output anilluminating beam of an operating wavelength toward a discrete spot in afield ahead of the illumination source; a bulk imaging optic 130characterized by a focal plane opposite the field; an aperture layercoincident the focal plane, defining a set of apertures 144 in a secondrectilinear grid array proportional to the first rectilinear grid array,and defining a stop region 146 around the set of apertures 144, eachaperture in the set of apertures 144 defining a field of view in thefield coincident a discrete spot output by a corresponding illuminationsource in the set of illumination sources 110, the stop region 146absorbing light rays reflected from surfaces in the field outside offields of view defined by the set of apertures 144 and passing throughthe bulk imaging optic 130; a set of lenses 150, each lens in the set oflenses 150 characterized by a second focal length, offset from the focalplane opposite the bulk imaging optic 130 by the second focal length,aligned with an aperture in the set of apertures 144, and configured tocollimate light rays passed by the aperture; an optical filter 160adjacent the set of lenses 150 opposite the aperture layer andconfigured to pass light rays at the operating wavelength; a set ofpixels 170 adjacent the optical filter 160 opposite the set of lenses150, each pixel in the set of pixels 170 aligned with a subset of lensesin the set of lenses 150; and a diffuser 180 interposed between theoptical filter 160 and the set of pixels 170 and configured to spreadcollimated light output from each lens in the set of lenses 150 across acorresponding pixel in the set of pixels 170.

Generally, in this variation, the system includes a two-dimensional gridarray of channels (i.e., aperture, lens, and pixel sets or lens tube andpixel sets) and is configured to image a volume occupied by the systemin two dimensions. The system can collect one-dimensional distancedata—such as counts of incident photons within a sampling period and/ortimes between consecutive photons incident on pixels of known positioncorresponding to known fields of view in the field—across atwo-dimensional field. The one-dimensional distance data can then bemerged with known positions of the fields of view for each channel inthe system to reconstruct a virtual three-dimensional representation ofthe field ahead of the system.

In this variation, the aperture layer can define a grid array ofapertures, the set of lenses 150 can be arranged in a similar grid arraywith one lens aligned with one aperture in the aperture layer, and theset of pixels 170 can include one pixel per aperture and lens pair, asdescribed above. For example, the aperture layer can define a 24-by-24grid array of 200-μm-diameter apertures offset vertically and laterallyby an aperture pitch distance of 300 μm, and the set of lenses 150 cansimilarly define a 24-by-24 grid array of lenses offset vertically andlaterally by a lens pitch distance of 300 μm. In this example, the setof pixels 170 can include a 24-by-24 grid array of 300-μm-square pixels,wherein each pixel includes a 3×3 square array of nine 100-μm-squareSPADs.

Alternatively, in this variation, the set of pixels 170 can include onepixel per group of multiple aperture and lens pairs. In the foregoingexample, the set of pixels 170 can alternatively include a 12-by-12 gridarray of 600-μm-square pixels, wherein each pixel includes a 6×6 squarearray of 36 100-μm-square SPADs and wherein each pixel is aligned with agroup of four adjacent lenses in a square grid. In this example, foreach group of four adjacent lenses, the diffuser 180: can biascollimated light rays output from a lens in the (1,1) position in thesquare grid upward and to the right to spread light rays passing throughthe (1,1) lens across the full breadth and width of the correspondingpixel; can bias collimated light rays output from a lens in the (2,1)position in the square grid upward and to the left to spread light rayspassing through the (2,1) lens across the full breadth and width of thecorresponding pixel; can bias collimated light rays output from a lensin the (1,2) position in the square grid downward and to the right tospread light rays passing through the (1,2) lens across the full breadthand width of the corresponding pixel; and can bias collimated light raysoutput from a lens in the (2,2) position in the square grid downward andto the left to spread light rays passing through the (2,2) lens acrossthe full breadth and width of the corresponding pixel, as shown in FIG.8.

In the foregoing example, for each group of four illumination sources ina square grid and corresponding to one group of four lenses in a squaregrid, the system can actuate one illumination source in the group offour illumination sources at any given instance in time. In particular,for each group of four illumination sources in a square gridcorresponding to one pixel in the set of pixels 170, the system canactuate a first illumination source 111 in a (1,1) position during afirst sampling period to illuminate a field of view defined by a firstaperture 141 corresponding to a lens in the (1,1) position in thecorresponding group of four lenses, and the system can sample all 36SPADs in the corresponding pixel during the first sampling period. Thesystem can then shut down the first illumination source 111 and actuatea second illumination source 112 in a (1,2) position during a subsequentsecond sampling period to illuminate a field of view defined by a secondaperture 142 corresponding to a lens in the (1,2) position in thecorresponding group of four lenses, and the system can sample all 36SPADs in the corresponding pixel during the second sampling period.Subsequently, the system can then shut down the first and secondillumination sources 112 and actuate a third illumination source in a(2,1) position during a subsequent third sampling period to illuminate afield of view defined by a third aperture corresponding to a lens in the(2,1) position in the corresponding group of four lenses, and the systemcan sample all 36 SPADs in the corresponding pixel during the thirdsampling period. Finally, the system can shut down the first, second,and third illumination sources and actuate a fourth illumination sourcein a (2,2) position during a fourth sampling period to illuminate afield of view defined by a fourth aperture corresponding to a lens inthe (2,2) position in the corresponding group of four lenses, and thesystem can sample all 36 SPADs in the corresponding pixel during thefourth sampling period. The system can repeat this process throughoutits operation.

Therefore, in the foregoing example, the system can include a set ofpixels 170 arranged across an image sensor 7.2 mm in width and 7.2 mm inlength and can implement a scanning schema such that each channel in thesystem can access (can project light rays onto) a number of SPADsotherwise necessitating a substantially larger image sensor (e.g., a14.4 mm by 14.4 mm image sensor). In particular, the system canimplement a serial scanning schema per group of illumination sources toachieve an exponential increase in the dynamic range of each channel inthe system. In particular, in this variation, the system can implementthe foregoing imaging techniques to increase imaging resolution of thesystem.

In the foregoing implementation, the system can also include a shutter182 between each channel and the image sensor, and the system canselectively open and close each shutter 182 when the illumination sourcefor the corresponding channel is actuated and deactivated, respectively.For example, the system can include one independently-operableelectrochromic shutter 182 interposed between each lens, and the systemcan open the electrochromic shutter 182 over the (1,1) lens in thesquare-gridded group of four lenses and close electrochromic shutters182 over the (1,2), (2,1), and (2,2) lens when the (1,1) illuminationsource is activated, thereby rejecting noise passing through the (1,2),(2,1), and (2,2) lens from reaching the corresponding pixel on the imagesensor. The system can therefore selectively open and close shutters 182between each channel and the image sensor to increase SNR per channelduring operation. Alternatively, the system can include oneindependently-operable electrochromic shutter 182 arranged over selectregions of each pixel, as shown in FIG. 8, wherein each electrochromicshutter 182 is aligned with a single channel (i.e., with a single lensin the set of lenses). The system can alternatively include MEMSmechanical shutters or any other suitable type of shutter interposedbetween the set of lenses 150 and the image sensor.

In this variation, the system can define two-dimension grid arrays ofapertures, lenses, diffusers, and/or pixels characterized by a firstpitch distance along a first (e.g., X) axis and a second pitchdistance—different from the first pitch distance—along a second (e.g.,Y) axis. For example, the image sensor can include pixels offset by a 25μm horizontal pitch and a 300 μm vertical pitch, wherein each pixelincludes a single row of twelve subpixels.

However, in this variation, the two-dimensional optical system caninclude an array of any other number and pattern of channels (e.g.,apertures, lenses (or lens tubes), and diffusers) and pixels and canexecute any other suitable scanning schema to achieve higher spatialresolutions per channel than the raw pixel resolution of the imagesensor. The system can additionally or alternatively include aconverging optic, a diverging optic, and/or any other suitable type ofoptical element to spread light rights passed from a channel across thebreadth of a corresponding pixel.

As a person skilled in the art will recognize from the previous detaileddescription and from the figures and claims, modifications and changescan be made to the embodiments of the invention without departing fromthe scope of this invention as defined in the following claims.

What is claimed is:
 1. An optical channel for receiving photons anddetecting the photons comprising: a bulk imaging optic; an aperturelayer located at an imaging plane of the bulk optic; a collimating lenslayer behind the aperture layer and separated therefrom by a focallength of the collimating lens layer; an optical filter behind thecollimating lens layer; and a pixel offset from the optical filteropposite the collimating lens layer, and responsive to photons incidenton the pixel.
 2. The optical channel of claim 1 further comprising adiffuser that spreads light rays passed from the aperture layer throughthe optical filter across an area of a corresponding pixel, whereby thepixel can detect incident photons across its full width and height toincrease the dynamic range of the system.
 3. The optical channel ofclaim 1 wherein the pixel comprises at least one single-photon avalanchediode detector.
 4. The optical channel of claim 1 wherein the pixelcomprises at least one resonant cavity photodiodes.
 5. A set of opticalchannels of claim 1 having the set of pixels of the set of opticalchannels being arranged on a single image sensor.
 6. The set of opticalchannels of claim 5 wherein multiple sets of optical channels arefabricated on the same wafer and diced to yield multiple sets of opticalchannels.
 7. The set of optical channels of claim 5 further comprising abulk imaging optic having apertures at a focal plane projected into afield defining fields of view for each optical channel.
 8. The set ofoptical channels with the bulk imaging optic of claim 7 furthercomprising a bulk transmitter optic having a set of optical emitters ata focal plane projecting light into a field defining transmitter fieldsof view that are overlapping with the fields of view defined by the setof optical channels, and operating at a same wavelength as the set ofoptical channels and a controller to form an active illumination opticalsensor.
 9. The active illumination optical sensor of claim 8 having theset of optical emitters being arranged on a single semiconductor die.10. The active illumination optical sensor of claim 8 having the set ofoptical emitters being lasers.